Method of utilizing a cerebral instrument guide frame

ABSTRACT

A cerebral instrument guide includes first and second arcs with aligned openings adjacent their ends, the openings defining a common axis about which the arcs are pivotal. The rods are mounted for movement along the common axis into contact with a human patient&#39;s auditory meati. A nasal bridge fixation element mounted on the first arc, as well as orbit pads, engage the bridge of a patient&#39;s nose, and his/her bony orbits. The appropriate angle to which the arcs should be pivoted with respect to each other is calculated by a computer program, as is the position to which a tubular instrument guide, slidable along the second arc and a projection from it intersecting the mid point of the common axis, is to be positioned to mark the burr hole on the patient&#39;s skull for performing a neurological procedure, such as a ventriculostomy. A needle is passed through the tubular instrument guide to mark the burr hole site. The cerebral instrument guide frame may be left in place, or removed, while a stereotactic instrument placement guide is used (after the burr hole is formed) to properly position the neurological instrument (e.g. catheter) used to perform the neurological procedure.

This application is a divisional of application Ser. No. 08/062,633,filed May 18, 1993, now U.S. Pat. No. 5,330,485, which in turn is acontinuation-in-part of application Ser. No. 07/786,278 filed Nov. 1,1991 now U.S. Pat. No. 5,300,080, issued Apr. 5, 1994.

BACKGROUND AND SUMMARY OF THE INVENTION

There are many neurological procedures which require the accurateplacement of a neurological instrument, including for biopsy,radioactive seed placement, and lesion generation. One of the mostcommon neurological procedures requiring accurate placement is aventriculostomy procedure in which a cerebral ventricle drain or shuntis installed. Such a drain or shunt is utilized for ventricular drainagewhen a patient manifests hydrocephalus resulting from congenital brainmalformations, acute or chronic infections, tumors, intraventricularhemorrhage, or normal pressure hydrocephalus.

Conventional procedures for the placement of ventricular drains orshunts rely heavily on the skill of the neurosurgeon, and/or arerelatively expensive and time consuming. After a CT scan, or otherimaging, the neurosurgeon forms a burr hole in the skull, and then theneurosurgeon guides a catheter through the burr hole toward landmarks onthe opposite side of the patient's head. It is necessary that theneurosurgeon be able to completely accurately visualize the internaltomography of the brain when performing this procedure, and it ispresumed that the catheter is properly located when the surgeon obtainsfluid returned through the catheter. In some circumstances, theneurosurgeon feels it advisable to check the location of the catheter,and for that purpose the patient must be subjected to another CT scan ofthe brain in order to verify proper location of the catheter. Since eachseparate, individual, CT scan is expensive, and since the prior artprocedures are time consuming both for the neurosurgeon and theanaesthesiologist, there has long been a need for procedures moreregularly and inexpensively accurately placing ventricular drain orshunt catheters, which will result in longer shunt patency and decreasedmorbidity due to shunt malposition.

According to one aspect of the invention of the parent application, astereotactic neurological instrument placement guide is provided thatmay be utilized in numerous different types of neurological procedures,and which has ideal suitability for use in ventriculostomy procedures.The guide according to the invention is simple to construct and toutilize, and can readily enhance accuracy, reduce time, increaseconfidence, and reduce cost for a given level of confidence, inventriculostomy procedures and other neurological treatment methods.

The stereotactic guide of the parent application has only first andsecond skull engaging point members, which have a common central axis. Aframe mounts the skull engaging point members for controlled movementwith respect to each other along the central axis. Means are provideddefining a linear guide passage in the first point member, a straightline extension of the linear guide passage extending along a commoncentral axis, and the linear guide passage is large enough for thepassage of a neurological instrument (e.g. catheter or shunt) throughit. The termination of the first point member coaxial with the linearpassageway and common central axis provides for stabilizing the firstpoint member in a burr hole; for example the termination may comprise atruncated cone.

The point members may be attached to arms, which in turn are attached toa guide sleeve and a guide element (bar or rod) which are movable withrespect to each other. A locking screw can lock them in a position towhich they have been moved, or they may be biased toward each other byan elastic band, spring loading, or the like. The means defining alinear passage may comprise a slotted sleeve rigidly fixed to the framearm, with a slotted tubular element received within the sleeve androtatable from one position in which the slots of the sleeve and tubularmember are not aligned, to a second position in which the slots arealigned. When the slots are not aligned, the guide passage is closed andprovides positive guiding of the catheter therethrough. When the slotsare aligned, the placement guide may be removed from contact with thepatient's skull, and the catheter.

According to the parent application, the key to proper utilization ofthe stereotactic neurological instrument placement guide is the properlocation of the fixing point on the opposite side of the patient's skullfrom the burr hole. The positive location of the fixing point, whichwill receive the second point member of the placement guide, oppositethe proposed site for the burr hole is determined utilizing a CT scan,magnetic resonance imaging (MRI), or another type of coordinatemultiplanar tomographic imaging of the patient's skull. Utilizing X, Y,and Z coordinates for the burr hole (marked by a nipple marker or thelike), and determining the coordinates of the particular portion of theventricle, or other location within the brain, desired to be acted uponby the neurosurgeon, the data from the imaging can be used to calculatethe loci of points along a straight line between the burr hole and thetarget area, which loci can be extended to the patient's skull on theopposite side thereof from the burr hole, and that part of the patient'sskull can be marked with a nipple marker, oil, or the like. Thecalculations are preferably provided by vector parameterization,utilizing a programmable scientific calculator, and the gantry angle ofthe imaging equipment can be automatically accommodated.

Desirably the distance of the target point from the burr hole is alsocalculated according to the invention, so that the neurosurgeon can useindicia on the catheter to determine when the catheter has been insertedthe distance necessary to properly position it at the target. Practicingthe method according to the invention, since the placement of the fixingpoint is accurately determined, there is no necessity for a second CTscan, or the like.

While the invention will be described herein primarily with respect toventriculostomy procedures, it is to be understood that both theapparatus and procedures according to the invention may be applied to awide variety of neurological practices. In fact, the basic positioningfacilitating features of the parent application are applicable not justto neurosurgery, but in general to determining the position of a linebetween two points on or within a human patient's body utilizing datanormally determined from a coordinate multiplanar tomographic imaging(CT, MRI, etc.) of the patient's body during which the patient isdisposed at an angle, and is incrementally advanced between images.Utilizing the present invention it is possible to practice proceduresnot heretofore contemplated, or to maximize the accuracy of presentprocedures, since according to the invention it is possible toaccurately locate and determine the coordinates of two or more points onor within a human body (e.g. within the brain).

Also according to the present invention, the utility of the stereotacticneurological instrument placement guide described above is improved byutilization of a cerebral instrument guide frame and supporting computerprograms. The cerebral instrument guide frame, and related procedures,according to the invention allow the neurosurgeon to mark the burr holesite and fixing point on the patient in the operating suite prior toapplying the stereotactic instrument guide described above. Thiseliminates the need to mark these sites on the patient in themultiplanar tomographic imaging (CT scanning) suite. In this way it ispossible to avoid accidental erasure or movement of identifying marks ormarkers placed by the radiologist. Further, instead of having a mark onthe scalp, the neurosurgeon can directly mark the patient's skull,improving accuracy of the stereotactic instrument guide described above.

The cerebral instrument guide frame according to the present inventionis preferably mounted in the patient's ears and on the bridge of thepatient's nose. In addition to allowing--in association with thecomputer programs described hereafter--accurate location of the burrhole and fixing point, the cerebral instrument guide frame can serve asa fixing point for the stereotactic instrument guide described earlier.The cerebral instrument guide frame according to the invention thusprovides a neurosurgeon a simple stereotactic method for catheterplacement, or for other neurological procedures, and expands the utilityof the stereotactic instrument guide described above.

A cerebal instrument guide frame for use with a live human patientaccording to the present invention comprises the following elements: Afirst arcuate member having first and second ends, and a radius. Asecond arcuate member having first and second ends and a radius, (theradius of the second arcuate member being greater than the radius of thefirst arcuate member). Aligned first and second openings providedadjacent each of the first and second ends of each of the first andsecond arcuate members. First and second rigid ear fixator rods mountedin the aligned openings, the first in the openings adjacent the firstends of the first and second arcuate members, and the second in theopenings adjacent the second ends of the first and second arcuatemembers, the rods mounted for movement with respect to the first andsecond arcuate members along a common axis passing through the openings,and the arcuate members mounted for pivotal movement with respect toeach other about the common axis. An abutment mounted on one of thearcuate members for engaging a portion of a patient's head to precludemovement of the arcuate member past that portion of the patient's head.And an instrument guide mounted on the other of the arcuate members forguiding an instrument aligned therewith into contact with the patient'shead, the guide directed to the midpoint of the common axis.

The abutment preferably comprises a nasal bridge fixation element forengaging the bridge of a patient's nose, and the instrument guidecomprises a tubular element mounted to one of the arcuate elements formovement with respect to that element along the arcuate extent thereof.The abutment is mounted on the first arcuate element and the instrumentguide on the second arcuate element. A pair of orbit pads also may bemounted on the first arcuate element on opposite sides of the nasalbridge fixation element for engaging the patient's orbits. The tubularinstrument guide element has an internal diameter slightly greater thanthe external diameter of a needle. The first and second arcuate memberseach preferably comprise a hemicircle, or semicircle, and the nasalbridge fixation element is mounted for radial movement with respect tothe first arcuate element (that is, along the radius thereof). The firstand second arcuate members preferably are made of aluminum, a rigiddurable sterilizable medical-grade structural plastic, or the like.

The cerebral instrument guide frame according to the invention may beused in combination with the stereotactic neurological instrumentplacement guide as described above, with one of the point members of theskull engaging elements of the stereotactic neurological instrumentguide engaging the tubular instrument guide element, and in alignmenttherewith. When the guide frame according to the present invention iscombined with the stereotactic neurological instrument placement guidedescribed above, typically the second point member comprises the "one ofthe point members", and the first and second arcuate members make anangle of about 160°-180° with respect to each other with the secondpoint member in alignment with the tubular instrument guide element.

According to another aspect of the present invention, a cerebralinstrument guide for use with a live human patient is provided whichcomprises the following elements: A first frame element having first andsecond ends, and a central portion. A nasal bridge fixation mounted onthe first frame element at the central portion, and movable with respectto the first frame element. A second frame element having first andsecond ends, and a central portion. Pivot means for mounting the firstand second frame elements for pivotal movement with respect to eachother about a common axis. An instrument guide mounted on the secondframe element, and movable with respect thereto and directed toward themidpoint of the common axis. And means for positively locating the pivotmeans with respect to the patient's head so that the axis remainsstationary with respect to a predetermined portion of the patient'shead.

Typically, the pivot means and the positively locating means comprisefirst and second ear fixation rods adapted to be inserted into thepatient's ears and received within aligned openings in the first andsecond ends of the first and second frame elements. The rods may beslidable with respect to the frame elements to move toward and away fromthe patient's ears. The frame elements preferably comprise first andsecond hemicircles with the second frame element hemicircle having alarger radius than the first element hemicircle. The ear rods preferablyhave some covers--where they engage the patient's ears--of a softmaterial, such as soft rubber, to allow seating of the rod ends into theexternal auditory meatia.

The computer program utilized with the present invention accepts datafrom computed tomographic images representing five separate points: atarget point in a cerebral ventricle, a point representing the intendedburr hole site on the skull, a point at the right external auditorymeatus, a point at the left external auditory meatus, and a pointrepresenting the interior superior edge of either bony orbit. Theprogram corrects for CT scanner gantry tilt and then calculates an angleat which to separate and set the first and second arcs of the cerebralinstrument guide frame, and an angle between a line containing themidpoint of the line in space (the common axis of the arcuate members)and the skull point, and a line in space connecting the ends of thearcs. The sliding instrument guide mounted on the second arcuate memberis set at this calculated angle, and directed toward the skull.

When the apparatus described above is utilized, the patient first has aCT scan (or other multiplanar tomographic imaging) of the brain andskull. Neither the cerebral instrument guide frame nor the stereotacticinstrument guide is mounted on the patient's head during the acquisitionof the CT data, but following the CT scan procedure, the target, burrhole, right and left auditory meatia, and orbital ridge points areentered into the computer program to calculate the angles necessary. Inthe operating room, with or without the patient under generalanesthesia, the cerebral instrument guide frame is then applied to thepatient's head by symmetrically advancing the rods connecting the arccentrally toward and into the external ear canals, and then by seatingthe mid-line U-shaped nasal bridge onto the nasion. The angle betweenthe first and second arcuate members and the position of sliding guidealong the first arc are set, and the neurosurgeon can then pass a longneedle down the sliding guide through the scalp and onto the skull atthe skull point where a distinguishing mark for the burr hole can bemade, and later for the fixing point. The cerebral instrument guideframe may then be removed and the stereotactic instrument guide used asa described above, or the cerebral instrument guide frame can be left inplaced and repositioned to accept the fixing point of the stereotacticinstrument guide.

According to another aspect of the present invention, a method ofpositively locating a burr hole site on a patient's skull during aneurological procedure on a human patient, using a guide comprisingfirst and second frame members mounted for pivotal movement with respectto each other about a common axis defined by ear fixators, one of theframe members having a nasal bridge fixation, and the other having aninstrument guide, is provided. The method comprises the steps of: (a)Effecting coordinate multiplanar tomographic imaging of the patient'shead. (b) During the practice of step (a) determining locations of thetarget in the patient's head, the burr hole site on the patient's skull,the patient's left and rights auditory medati, and at least one of thepatient's orbital ridges. (c) With a computer, calculating from the datadetermined in step (b) the angular positions of the frame members of theguide to mark the burr hole site and fixing point on the patient'sskull, and the proper position of the instrument guide along the secondframe member. Then (d) moving the ear fixations of the guide intopositive contact with the patient's ears, and the nasal bridge fixationinto positive contact with the patient's nasal bridge. And (e) movingthe second frame member of the guide frame with respect to the firstframe member to have the proper orientation to mark the burr hole site,and moving the instrument guide to the proper position along the secondframe member, and then marking the burr hole site using the instrumentguide.

The method can also be for positively locating a fixing point on thepatient's skull in which case there is the further step of (f) movingthe second frame member of the guide with respect to the first framemember to have the proper orientation to mark the fixing point on thepatient's skull, and then marking the fixing point site using theinstrument guide. Also, there may be the still further step, with theguide in place with the relative positions of the components as providedin step (f), of moving a stereotactic neurological placement guidehaving end point members into operative association with the burr holesite and the instrument guide on the second frame member; effectingformation of a burr hole; and passing an instrument through one of saidstereotactic neurological placement guide point members engaging saidburr hole, to pass the instrument to the target within the patient'sskull.

Alternatively, the guide is removed from the patient's ears and nose, aburr hole is formed at the burr hole site, and the end point members ofa stereotactic neurological placement guide having end point members ismoved into operative association with the burr hole site and a fixingsite opposite the burr hole site on the patient's skull. The neurlogicalinstrument is inserted through the burr hole and placement guide intooperative association with the target within the patient's skull.

Step (c) may be practiced in part by using vector parameterization, andstep (a) is practiced using a non-zero angle of inclination betweenimaging equipment and the patient while there is an incremental advancebetween images, the computations in step (c) taking into account theangle of inclination and the increment of advance between images.

In general, the invention facilitates and provides a method ofperforming a neurological procedure on a human patient utilizing ascanner, a Cerebral instrument guide frame, and an operating room, thatis greatly simplified with respect to the prior art, allowing thescanning to be done without a frame on the patient's head, and avoidingthe expense and time delay of moving a patient from the operating roomback to the scanner, and running a second scan on the patient with aframe attached to the patient's head. This aspect of the method of theinvention comprises the steps of substantially sequentially: (a)Effecting coordinate multiplanar tomographic imaging of the patient'shead with the scanner while the patient's head is free of frameattachments, to obtain data necessary for performing a neurologicalprocedure. (b) Moving the patient to the operating room. (c) In theoperating room, utilizing the data from step (a), fixing the cerebralinstrument guide frame on the patient's head; and (d) substantiallyimmediately after step (c), in the operating room, without transportingthe patient back to the scanner to effect a second imaging, performingthe neurological procedure on the patient, utilizing the cerebralinstrument guide frame to guide one or more medical instruments (e.g.catheter, light pipe, laser, etc.).

It is a primary object of the present invention to provide an accurate,effective, and simplified manner of performing neurlogical procedures ona human patient. This and other objects of the invention will becomeclear from an inspection of the detailed description of the inventionand from the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of an exemplary stereotactic neurologicalinstrument placement guide according to the invention;

FIG. 2 is a side exploded view, partly in elevation and partly incross-section, of the components associated with the first skullengaging point member of the stereotactic neurological instrumentplacement guide of FIG. 1;

FIG. 3 is an end view of a second embodiment of the second skullengaging point member of the stereotactic neurological instrumentplacement guide of FIG. 1;

FIG. 4 illustrates a pair of nipple markers that may be utilized in thepractice of the method of the invention, one shown in top perspectiveand the other in bottom perspective; .

FIG. 5 is a schematic view showing the stereotactic neurologicalinstrument placement guide of FIG. 1 in use on a patient's head with acatheter having been placed by the stereotactic neurological instrumentplacement guide;

FIG. 6 is a schematic view of conventional coordinate multiplanartomographic imaging equipment utilized in the practice of the methodaccording to the invention;

FIG. 7 is a schematic view of a screen of the apparatus of FIG. 6 at oneof the slice locations;

FIG. 8 is a top plan view of a programmable calculator and recordkeeping pad mounted in a manner facilitating its utilization in apractice of the method according to the invention;

FIG. 9 is a top perspective view of an exemplary cerebral instrumentguide frame according to the present invention;

FIG. 10 is a side view of a patient's head with the cerebral instrumentguide frame of FIG. 9 shown in operative association therewith to mark aburr hole site;

FIG. 11 is a front view like that of FIG. 10; and

FIG. 12 is a view like that of FIG. 10 only showing the stereotacticneurlogical instrument placement guide of FIG. 1 mounted in associationwith the cerebral instrument guide frame and the burr hole site on thepatient's skull, for insertion of a catheter.

DETAILED DESCRIPTION OF THE DRAWINGS

FIGS. 1 and 5 illustrate an exemplary stereotactic neurologicalinstrument placement guide according to the invention, shown generallyat reference numeral 10. The guide 10 preferably is made of lightweight,rigid material, such as aluminum, titanium, hard plastic, or the like.It includes only two skull engaging elements, that is the skull engagingelements consist of a first skull engaging point member shown generallyby reference numeral 11, and a second skull engaging point member showngenerally by reference numeral 12. A frame mounts the members 11, 12 formovement toward and away from each other along a common central axis,preferably so that they move linearly with respect to each other alongthe linear axis 13. The frame preferably comprises a first arm 14, whichpreferably is rigidly connected to the first point member 11, and asecond arm 15 which preferably is rigidly connected to the second pointmember 12. Movement of the arms 14, 15 with respect to each other, withthe members 11, 12 along the axis 13, is preferably provided by a sleeve16 rigidly attached to the first arm 14, and a guide element, such as arod or bar, 17 rigidly connected to the second arm 15. The portions 15,17 can be formed integrally (as by molding), as can the portions 14, 16.

In most circumstances, it is desirable to either be able to lock theframe of the device 10 so that the members 11, 12 are positioned at aspecific distance from each other (corresponding to the dimension of thepatient's skull at the operative area of use), or means are provided forbiasing the arms 14, 15 toward each other, or for biasing the firstmember 11 toward the second member 12. Where locking is desired, athumbscrew 18 may be provided threaded through an opening in the guidesleeve 16 and releasably engaging the guide element 17. When the guideelement 17 is tightly engaged, relative movement between the arms 14, 15is not possible, but when the thumbscrew 18 is loosened relativemovement in a dimension parallel to the axis 13 is possible. Instead of,or in conjunction with, the thumb locking screw 18, an elastic band 19may be provided, which exerts a force pulling the arms 14, 15 towardeach other. Alternatively (not shown) a spring loading can be providedfor the first point member 11 itself, the spring loading operatingbetween the arm 14 and the end, skull engaging, termination 20 of themember 11, so that it is biased into contact with the patient's skull.

It is very desirable to be able to remove the guide 10 from contact withthe patient's skull, and from contact with the neurological instrument(e.g. catheter), once the stereotactic device 10 has been utilized toproperly guide the neurological instrument into place. This may beaccomplished by the means most clearly illustrated in FIG. 2.

FIG. 2 illustrates the first point member 11 as a slotted sleeve 22which is rigidly attached to the arm 14, with the slot 23 thereinpreferably on the opposite face of the sleeve 22 as the arm 14. Disposedwithin the sleeve 22 is the slotted tubular element 24, having a slot 25in one face thereof along the length thereof, both the slots 23 and 25having a width which is great enough so that a catheter 26, or otherneurological instrument, may be removed therethrough. Also, the internaldiameter of the tubular element 24 is such that it provides a relativelytight fit for the catheter 26, but so that the catheter can movelongitudinally therethrough. If the arm 14 is made of metal, it isdesirable to make the slotted sleeve of a similar metal, while it isdesirable to make the tubular member 24 of nylon, or a similarrelatively rigid, durable plastic with lubricity characteristics.

The position of the tubular element 24 within the slotted sleeve 22 canbe fixed by tightening the thumbscrew 27 which passes through the sidewall of the sleeve 22, perpendicular to the dimension of elongation ofthe interior passageway, and the slot 23, therein. End termination 20 ofthe tubular element 24 actually engages a burr hole in the skull, and ispreferably shaped in a manner so as to stabilize the first point memberwithin the burr hole. This can be accomplished, as illustrated in FIGS.1 and 2, by forming the termination 20 as a truncated cone.

Note that the catheter 26 preferably has indicia 28 formed along thelength thereof. The position of those indicia with respect to a fixedpoint on the device 10 (typically on the tubular element 24) can be usedas a guide by the neurosurgeon for insertion of the catheter 26 to makesure that it has been inserted to the proper position, i.e. so that thelead tip 29 thereof is at the target location in the brain ventricle orother target area.

It is preferred that the second skull engaging point member 12 merelycomprise a conical element terminating in a tip 30, which is integralwith or rigidly affixed to the arm 15. However, under some circumstancesit may be desirable to form the termination of the second point member12 so that it can surround a nipple marker, to facilitate accurateplacement. Such a second skull engaging point member is shown generallyby reference numeral 12' in FIG. 3, the member 12' being formed as ahollow truncated cone, with means defining an interior surface 31 whichis circular and has a diameter approximately equal to the outsidediameter of a nipple marker 32 (see FIG. 4).

FIG. 4 illustrates conventional nipple markers that may be utilized withthe device 10 to ensure proper positioning thereof in the surgicalprocedures according to the invention. The conventional nipple markers32 are discs of plastic, or like material that is not clearly visible ina CT, MRI, or other imaging procedure, with a small cylinder of lead (orlike radiopaque material) 33, having a diameter of about one-twomillimeters, on the top face 34, concentric therewith. The top face 34is smooth and uncoated, while the bottom face 35 has adhesive affixedthereto (it may have a release paper covering). In use, when a nipplemarker 32 is in place, a scribe mark on the skull can be provided bypassing a trocar or screw around disc 34. Alternatively, an entirenipple marker 32 may be used for placement, for example with respect tothe second point member 12' of FIG. 3.

FIG. 5 illustrates utilization of the device 10 in the placement of aventricular drain or shunt. Nipple markers 32 are placed where a burrhole 37 is to be formed in the patient's skull at a location determinedto be acceptable for the particular patient and procedure involved bythe neurosurgeon, and at a fixing point 38 on the opposite side of thepatient's skull from the burr hole 37. The manner in which the fixingpoint 38 is precisely located will be described hereafter.

The neurosurgeon moves the first arm 14 so that it is widely spaced fromthe second arm 15, and then moves the second point member 12 intooperative contact with the fixing point 38. Then the arm 14 is movedtoward the arm 15, with the members 11, 12 moving along a common linearaxis 13, until the termination 20 of the member 11 is stabilized withinthe burr hole 37. During this initial phase, the position of the arm 14with respect to the arm 15 may be fixed, and the tubular element 24 mayslide with respect to the slotted sleeve 22, or vice versa.

Once the termination 20 has properly stabilized within the burr hole 37,either the thumbscrew 18 can be tightened to lock the relative positionsof the arms 14, 15 in place (with the thumbscrew 27 likewise tightened),or the elastic band 19 can be placed around the arms 14, 15 to bias themtogether. When the device 10 is in this position, it is necessary to besure that the slots 23, 25 are misaligned with each other so that whenthe catheter 26 is passed therethrough it cannot move sidewardly out ofthe guide provided by the slotted sleeve 22 and tubular element 24.

With the device 10 thus so positioned, the neurosurgeon then moves thecatheter 26 into the guide provided by the sleeve 22 and element 24,inserting it into the skull until the appropriate indicia 28 is reached(e.g. at the top surface 39 of the element 24) indicating that thecatheter 26 has been inserted a distance calculated to be the distanceof the ventricle area to be drained from the burr hole 37.

Once the catheter 26 has been thus properly positioned it is desirableto be able to remove the device 10 from operative engagement with thepatient's head, and the catheter 26. This is accomplished by looseningthe thumbscrew 27, then rotating the tubular member 24 so that the slot25 therein is aligned with the slot 23 in the sleeve 22, the slots 23,25 providing a channel which is open, and then--with the terminationpoint 20 pulled away from the burr hole 37 (either by moving the tubularelement 24, or by moving the entire arm 14)--moving the device 10 in thedirection of the guide element 17 (that is away from the patient's head)so that the catheter passes through the channel defined by the slots 23,25. Thus the catheter 26 remains in place while the device 10 iscompletely detached.

It is to be understood that a wide variety of modifications may be madein the stereotactic placement guide 10. For example, the tubular element24 could be continuous, rather than slotted, and it could be removedfrom engagement with the catheter 26 by pulling it out over the top ofthe catheter 26, along the length thereof, and then the catheter 26moved out through the slot 23. Also the sleeve 22 could be pivotallyconnected to the arm 14, or detachably connected thereto, and a widevariety of other modifications are also possible.

According to the present invention, it is necessary to accuratelyposition the fixing point 38, otherwise the goals of accurate placementof the neurological instrument (e.g. catheter 26) will not be achieved.Accurate placement of the nipple marker 32, or the like, at the fixingpoint 38 is accomplished utilizing conventional coordinate multiplanartomographic imaging equipment, shown schematically generally byreference numeral 40 in FIG. 6, and by utilizing a programmablecalculator 41 (see FIG. 8), or a like computer.

The coordinate multiplanar tomographic imaging equipment 40 preferablyis CT or MRI equipment, but other coordinate multiplanar tomographicimaging techniques and equipment may also be utilized. Such equipment 40typically cooperates with a table 42 on which the patient rests, and theequipment 40 is disposed at a tilt or gantry angle 43 with respect totable 42 to ensure proper imaging. A computer control 44 controls theequipment 40, and desired information is viewable on the screen 45.During the imaging operation, the table 42 is incrementally advanced inthe Z dimension illustrated in FIG. 6.

When the patient is placed in the equipment 40, a nipple marker 32 orthe like for the burr hole 37 is in place (being shown in an exaggeratedsize in FIG. 6). Utilizing the equipment 40, the operator determines theX, Y, and Z (Z being the position along the table 42) coordinates ofthat location, which is a first point. The equipment 40 operator willhave already been instructed by the neurosurgeon as to what the targetlocation in the brain has been decided upon. For example the targetlocation may be a particular second point 47 (see FIG. 7, arepresentation of an image of the patient's skull on the screen 45 atone particular slice) within the ventricle 48. The coordinates of thesecond point 47 are also determined by the operator as is conventional.

The operator operates the equipment 40 to conduct a conventional imagingoperation, e.g. CT scan. On the screen 45 all of the data associatedwith each slice of the imaging operation is recorded, including theposition along the table 42 (the dimension Z) and the table moves anincrement between each slice, the increment typically being about 5 to10 millimeters.

Utilizing the coordinates of the first point 32, 37 and the second point47 (the X, Y and Z coordinates of each), the angle of inclination 43 ofthe scanning equipment 40 with respect to the table 42 (the gantryangle), and the incremental advancement (the incremental advance indimension Z, typically 5 millimeters), the distance between the firstand second points can be calculated, and the loci of points along a linecontaining the first and second points can be determined, the line beingshown schematically at 50 in FIG. 7. This calculation is performedutilizing the programmable calculator 41 or like computer, utilizingvector parameterization. FIG. 7 illustrates the points 32, 47, 38 all onthe same screen only for the purposes of facilitating the description ofthe invention. However, in a real life use no single screen ("slice")will contain all three points since they are not coplanar with the"slices".

Pursuant to vector parameterization, as is well known per se in vectormathematics, for any line passing through a volume a vectorparameterization for the line can be derived utilizing the equationr(t)=a+tb where t is real and r, a and b are nonzero vectors. Vector "a"passes from the origin of the coordinate system to a point on the lineto be described. Vector b is on the line and gives the line direction. tis a scalar which ranges over the set of real numbers. Varying t variesthe vector r(t), but the tip of r(t) remains on the line described.Given any two points in the cartesian coordinate system, a line throughthese two points can be described using the vector parameterization. Theline can then be extended through space by changing the scalar value t.

A representation of the various program steps that will performed by thecalculator 41 in calculating the desired data is provided by thefollowing BASIC computer program:

    ______________________________________                                         10 INPUT "BURR HOLE TABLE POSITION", C                                        20 INPUT "BURR HOLE X VALUE", A                                               30 INPUT "BURR HOLE Y VALUE", B                                               40 INPUT "TARGET CT TABLE POSITION", Z                                        50 INPUT "TARGET X VALUE", X                                                  60 INPUT "TARGET Y VALUE", Y                                                  70 INPUT "CT TABLE INCREMENT", M                                              80 INPUT "CT GANTRY ANGLE (DEGREES)", L                                       90 N = M*COS(L)                                                              100 E = C*SIN(L) + B                                                          110 F = C*COS(L)                                                              120 V = Z*SIN(L) + Y                                                          130 W = Z*COS(L)                                                              140 D = CINT( (X - A).sup.2 + (V - E).sup.2 + (W - F).sup.2 ).sup.1/2         150 PRINT "BURR HOLE TO TARGET DISTANCE"                                      160 PRINT D; "MM"                                                             170 P = W - (10*N)                                                            180 FOR H = 1 TO 20                                                           190 K = (P - F)/(W - F)                                                       200 Q = CINT (A + (X - A)*K)                                                  210 R =  E + (V - E)*K                                                        220 S = F + (W - F)*K                                                         230 U = CINT(S/COS(L))                                                        240 T = CINT(R - U*SIN(L))                                                    250 PRINT "TABLE POSITION=";U;",";"X=";Q;",";"Y=";T                           260 P = P + N                                                                 270 NEXT H                                                                    280 STOP                                                                      ______________________________________                                    

Line 10 is the input for the burr hole Z coordinate, line 20 for theburr hole X coordinate, and line 30 for the burr hole Y coordinate. Line40 is for the target (second point 47) Z coordinate, line 50 for thetarget X coordinate, and line 60 for the target Y coordinate. Thecalculation in line 90 thus converts the CT table increments in theoriginal coordinate system to Z-axis movement increments in a newcoordinate system. Calculation 100 converts the burr hole Y value to thenew coordinate system, and line 20 converts the burr hole Z value.Calculation 120 converts the Y value of the target to the new coordinatesystem, and calculation 130 the Z target value. Calculation 140 is thedistance of the burr hole (37) to the target (47), with the function"CINT" being a round off function ("cut integer"), which is preferablyemployed. This distance is printed out at 150.

Calculation 170 is the calculation of the Z value 10 incrementalmovements from the target Z value in the new coordinate system. Theinstruction on line 180 initiates the loop in the computer program.Calculation 190 determines the conversion factor for a point on a vectorin three D space, calculation 200 determines the new X value for aparallel plane -10+0+10 incremental movements from the plane containingthe target point (47). Calculation 210 is the new Y value for theabove-mentioned parallel plane, while 220 is the calculation for the newZ value for the above-mentioned parallel plane. In calculation 230 thenew Y value is converted to the original coordinate system, whilecalculation 240 converts the new Z value to the original coordinatesystem. Calculation 260 determines the new parallel plane Z value oneincremental movement in the new coordinate system. Line 270 is theclosing loop statement, and after H 1 to 20 has been run, 280 providesthe end of program.

In the original coordinate system. An exemplary printout provided onceall of the H values have been run(step 250 is completed for H 1 to 20),and the CT scan is complete, is as follows (this provides the loci ofpoints on the calculated coordinate line):

    ______________________________________                                        71 MM                                                                         TABLE POSITION = 150, X = 50, Y = 45                                          TABLE POSITION = 145, X = 48, Y = 43                                          TABLE POSITION = 140, X = 45, Y = 40                                          TABLE POSITION = 135, X = 43, Y = 38                                          TABLE POSITION = 130, X = 40, Y = 35                                          TABLE POSITION = 125, X = 37, Y = 32                                          TABLE POSITION = 120, X = 35, Y = 30                                          TABLE POSITION = 115, X = 33, Y = 27                                          TABLE POSITION = 110, X = 30, Y = 25                                          TABLE POSITION = 105, X = 27, Y = 22                                          TABLE POSITION = 100, X = 25, Y = 20                                          TABLE POSITION = 95, X = 22, Y = 17                                           TABLE POSITION = 90, X = 20, Y = 15                                           TABLE POSITION = 85, X = 17, Y = 12                                           TABLE POSITION = 80, X = 15, Y = 10                                           TABLE POSITION = 75, X = 12, Y = 7                                            TABLE POSITION = 70, X = 10, Y = 5                                            TABLE POSITION = 65, X = 7, Y = 2                                             TABLE POSITION = 60, X = 5, Y = 0                                             TABLE POSITION = 55, X = 2, Y = -3                                            Break in 280                                                                  Ok                                                                            ______________________________________                                    

The printout provided above may be accomplished utilizing a stand aloneprinter connected to the calculator 41, or by a printer associated withthe calculator 41.

Utilizing the printout of table positions as provided above, theoperator of the equipment 40, 41, can determine the most likely positionfor the third point 38. Then, with the patient still in the scanner (nothaving been removed from the equipment the operator can return the table42 to the desired position, train on a laser light which shows a line onthe skull, then put on a nipple marker 32 at fixing point 38, and repeatthe slice at that table position. Only if the new slice indicatesmisalignment of the fixing point 38 need the nipple marker 32 berepositioned.

The data obtained from running the equipment 40, 41 for a particularpatient is preferably recorded, such as by utilizing the pad 52 mountedon the board 53 with the programmable calculator 41, to keep with thepatient's file. A writing implement 54 may also be mounted on the board53, providing an effective tool for facilitating the proceduresaccording to the invention.

While the exemplary methods according to the invention have beendescribed above with particular reference to a ventriculostomy procedurefor a human patient, it is to be understood that the procedures areapplicable to other neurological methods, such as biopsy, radioactiveseed placement, and lesion generation. In general, according to thepresent invention a neurological instrument placement procedure for ahuman patient, utilizing an instrument guide having opposed pointmembers disposed on a common linear axis, is provided, comprising thesteps of substantially sequentially: (a) Marking the proposed positionof a burr hole on the patient's skull. (b) Deciding upon the location ofa target point within the patient's skull. (c) Effecting coordinatemultiplanar tomographic imaging (e.g. CT, MRI, etc.) of the patient'sskull and brain. (d) Utilizing data from step (c), calculating acoordinate line between the burr hole proposed position and the targetpoint. (e) Utilizing the calculated coordinate line, determining afixing point on the patient's skull opposite the proposed position ofthe burr hole, and marking that fixing point on the patient's skull. (f)Forming a burr hole in the patient's skull at the marked proposed burrhole position. (g) Placing the instrument guide into operativeassociation with the patient's skull so that the opposed point membersengage the burr hole and the fixing point. (h) Passing a neurologicalinstrument into the burr hole, positively guided by the instrumentguide, along the common linear axis of the opposed point members, untilthe instrument reaches the target point. And, (i) performing aneurological procedure with the neurological instrument at the targetpoint.

The vector parameterization described above, according to the invention,is applicable to other medical procedures besides neurologicalprocedures. The vector parameterization according to the invention isutilizable in general for determining the position of a line (typicallya straight line) between two points on or within a human patient's bodyutilizing data normally determined from a coordinate multiplanartomographic imaging of the patient's body during which the patient isdisposed at a non-zer angle and while there is an incremental advancebetween images. Such a method comprises the following steps: (a) Duringcoordinate multiplanar tomographic imaging of the patient's body,determining the coordinates of a first point on or within the patient'sbody. (b) During coordinate multiplanar tomographic imaging of thepatient's body, determining the coordinates of a second point on orwithin the-patient's body. (c) Determining the non-zero angle ofinclination of the patient and the incremental advance between images.And, (d) utilizing the coordinates of the first and second points, thenon-zero angle of inclination, and the incremental advance, by vectorparameterization calculating the distance between the first and thesecond points and the loci of points along a line containing the firstand second points.

In order to improve the utility of the stereotactic neurologicalinstrument placement guide illustrated in FIGS. 1 through 5, anddescribed above, the cerebral instrument guide frame 56, illustrated inFIGS. 9 through 12, is provided, as well as a computer programassociated therewith.

The cerebral instrument guide frame 56 comprises the first frame member57 and a second frame member 58. Preferably both frame members 57, 58are arcuate, e.g. hemi-circular or semicircular, having a radius, withthe radius of the second arcuate member 58 greater than that of thefirst arcuate member 57. The member 57 has first and second ends 59, 60respectively, while the member 58 has first and second ends 61, 62respectively. These ends 59-62 have aligned openings 63-66,respectively, therein, the openings 63-66 defining a common axis 67.

Mounted within the openings 63, 65 is a first rigid ear fixator rod 68,and mounted within the openings 64, 66 is a second such rod 69. The rods68, 69 preferably have soft material, indicated by the soft rubbercoverings 70, 71, covering the inner ends thereof which are adapted toengage and seat into the external auditory meati of a human patient'shead, as illustrated in FIGS. 10 through 12. The rods 68, 69 areslidable along the axis 67 to accommodate patient's having differenthead sizes, and also to ensure positive seating in the patient's ears.The sliding action may be achieved merely by providing a friction fitbetween the openings 63-66 and rods 68, 69, or--as illustrated in FIG. 9in order to ensure that the relative positions of the members 57, 58 donot move with respect to each other--by providing collars 72, 73 thatare attached to the ends 59-62 so as to not be linearly movable withrespect thereto while allowing pivotal rotation, utilizing any suitableconventional means (such as stops applied to the collars 72, 73 onopposite sides of the ends 59-62 after proper location thereof withrespect to the collars 72, 73), with the rods 68, 69 received within thecollars 72, 73 and having a friction fit therewith so that they aremovable along the axis 67, but will remain in place in any position towhich they have been moved.

Mounted on the first arcuate member 57 is the adjustable nasal bridgefixation element shown generally by reference numeral 75. The element 75includes a curved inner end termination 76 adapted to engage the bridgeof a person's nose, as illustrated in FIGS. 10 through 12, and a shaft77 which extends radially with respect to the arcuate element 57. Theradial position of the curved end portion 76 may be adjusted byproviding the shaft 77 with a friction fit with respect to a sleeve 78(see FIG. 9) rigidly fixed to the element 57.

Also, the element 57 preferably has orbit pads 79 mounted thereon, onopposite sides of the nasal bridge fixation element 75, for engaging thepatient's orbits, these pads being shown by reference numeral 79 inFIGS. 9 and 11. The elements 79 also extend radially with respect to thearcuate element 57, and preferably pass through radial openings in theelement 57, having a friction fit therewith.

The frame 56 also includes, mounted on the second arcuate member 58, aninstrument guide 81, which is a substantially tubular element which isdirected to the mid point of the common axis 67. The internal diameteror cross-sectional area of the tubular element 81 is great enough toreceive a needle which is used for marking the burr hole site on apatient's skull. Preferably the position of the element 81 on the secondarcuate member 58 is adjustable along the arc, although the element 81always is directed to the mid point of the axis 67 regardless of itsposition with respect to the element 58. It is movably positioned withrespect to the element 58, for example, by rigid attachment thereof to acollar 82 (see FIG. 10) which makes a friction fit with the element 58(having the same arcuate radius thereof; the collar 82 may also be keyedto element 58).

In the utilization of the device 56 in a method of positively locatingthe burr hole site on a patient's skull during a neurological procedureon a human patient, it is desirable to calculate, with a computer, theangular positions of the frame elements 57, 58 with respect to eachother in order to properly mark the burr hole site. A computer programis utilized for this purpose. The program accepts data from computedtomographic images, represented as points in space, the following:target point in a cerebral ventricle, a point representing the intendedburr hole site on the skull, e point at the right external auditorymeatus, a point at the left external auditory meatus, and a pointrepresenting the interior superior edge of either bony orbit. Theprogram corrects for CT scanner non-zero gentry angle, and thencalculates an angle at which to separate the arcs 57, 58, this anglebeing shown by reference numeral 84 in FIG. 10. The program alsocalculates an angle between a line containing the mid point of the axis67 and the skull point, and the axis 67. The sliding guide 81 on thearcuate member 58 is then set at the second calculated angle, and thusthe sliding guide 81 is directed at the point on the skull--at the end85 of the element 81--where the burr hole site will be marked by passinga needle through the tubular guide 81.

In order to determine the correct angulation in degrees between thearcuate elements 57, 58 of the frame 56 for marking the skull burr holeposition, and optionally for accepting the fixing point of the elementof FIG. 1, the following computer program may be utilized:

    __________________________________________________________________________    10 INPUT "TARGET TABLE POSITION", C                                           20 INPUT "TARGET X VALUE", A                                                  30 INPUT "TARGET Y VALUE", B                                                  40 INPUT "BURR HOLE TABLE POSITION", F                                        50 INPUT "BURR HOLE X VALUE", D                                               60 INPUT "BURR HOLE Y VALUE", E                                               70 INPUT "RT EAC TABLE POSITION", I                                           80 INPUT "RT EAC X VALUE", G                                                  90 INPUT "RT EAC Y VALUE", H                                                  100 INPUT "LT EAC TABLE POSITION", L                                          110 INPUT "LT EAC X VALUE", J                                                 120 INPUT "LT EAC Y VALUE", K                                                 130 INPUT "BROW TABLE POSITION", P                                            140 INPUT "BROW X VALUE", M                                                   150 INPUT "BROW Y VALUE", N                                                   160 INPUT "GANTRY ANGLE IN DEGREES",                                          170 O = Q*3.14159/180                                                         180 R = C*SIN(O) + B                                                          190 S = C*COS(O)                                                              200 T = F*SIN(O) + E                                                          210 U = F*COS(O)                                                              220 V = I*SIN(O) + H                                                          230 W = I*COS(O)                                                              240 X = L*SIN(O) + K                                                          250 Y = L*COS(O)                                                              260 Z =  P*SIN(O) + N                                                         270 AA = P*COS(O)                                                             280 LL = (G + J)/2                                                            290 MM = (V + X)/2                                                            300 NN = (W + Y)/2                                                            310 BB =                                                                      (AA*X - AA*V + W*Z - W*X + Y*V - Y*Z)/(M*V - M*X + G*X - G*Z + J*Z -          J*V)                                                                          320 CC =                                                                      (AA*J - AA*G + W*M - W*J + Y*G - Y*M)/(Z*G - Z*J + V*J - V*M + X*M -          X*G)                                                                          330 DD =                                                                      (U*X - U*V + W*T - W*X + Y*V - Y*T)/(D*V - D*X + G*X - G*T + J*T - J*V)       340 EE =                                                                      (U*J - U*G + W*D - W*J + Y*G - Y*D)/(T*G - T*J + V*J - V*D + X*D - X*G)       350 FF = ((BB) 2 + (CC) 2 + (1)) .5                                           360 GG = ((DD) 2 + (EE) 2 +  (1)) .5                                          370 HH = ((BB*DD) + (CC*EE) + (1))/(FF*GG)                                    380 II = (1 - (HH) 2) .5                                                      390 JJ = ATN(II/HH)                                                           400 KK = ABS(JJ)*180/3.14159                                                  410 FA = CC*(Y - W) - 1*(X - V)                                               420 FB = 1*(J - G) - BB*(Y - W)                                               430 FC = BB*(X - V) - CC*(J - G)                                              440 FD = ((BB*D) - (BB*LL) + (CC*T) - (CC*MM) + (1*U) - (1*NN))               450 FE = ((FA*D) - (FA*LL) + (FB*T) - (FB*MM) +                               (FC*U) - (FC*NN))                                                             460 IF (FD > 0) AND (FE > 0) THEN PRINT "ARC ANGLE                            FOR BURR HOLE", CINT(KK)                                                      470 IF (FD > 0) AND (FE < 0) THEN PRINT "ARC ANGLE                            FOR BURR HOLE", CINT(-KK) + 180                                               480 IF (FD < 0) AND (FE > 0) THEN PRINT "ARC ANGLE                            FOR BURR HOLE", CINT(-KK)                                                     490 IF (FD < 0) AND (FE < 0) THEN PRINT "ARC ANGLE                            FOR BURR HOLE", CINT(KK) - 180                                                500 IF (FD < 0) AND (FE = 0) THEN PRINT "ARC ANGLE                            FOR BURR HOLE", "-90"                                                         510 IF (FD > 0) AND (FE = 0) THEN PRINT "ARC ANGLE                            FOR BURR HOLE", "90"                                                          520 IF (FD = 0) AND (FE < 0) THEN PRINT "ARC ANGLE                            FOR BURR HOLE", "-180"                                                        530 IF (FD = 0) AND (FE > 0) THEN PRINT "ARC ANGLE                            FOR BURR HOLE", "180"                                                         540 OO = (J - G)*(D - LL) + (X - V)*(T - MM) + (Y - W)*(U - NN)               550 PP = (((G - J)  2 + (V - X)  2 + (W - Y) 2) .5 *(((D - LL)                 2 + (T - MM)  2 + (U - NN) 2) .5)                                            560 QQ = OO/PP                                                                570 RR = (1 - (QQ)  2) -.5                                                    580 SS = ATN(RR/QQ)                                                           590 TT = SS*180/3.14159                                                       600 IF TT < 0 THEN TT = TT + 180                                              610 PRINT "SLIDE GUIDE ANGLE", CINT(TT)                                       620 UU = ((((A - D)  2 + (R - T)  2 + (S - U) - 2) *(200) 2 -                 ((A - D) 2 + (R - T) 2 + (S - U) 2)*((D - LL) 2 + (T - MM)                     2 + (U - NN)                                                                  2) + ((D - LL)*(A - D) + (T - MM)*(R - T) + (U - NN)*(S - U))                 2) .5 - ((D - LL)*(A - D) +                                                  (T - MM)*(R - T) + (U - NN)*(S - U)))/((A - D)                                 2 + (R - T) 2 + (S - U) 2)                                                   630 WWW = (D + (A - D)*UU)                                                    640 XXX = (T + (R - T)*UU)                                                    650 YYY = (U + (S - U)*UU)                                                    660 VV = (- (((A - D)  2 + (R - T)  2 + (S - U)  2)*(200)                      2 - ((A - D) 2 + (R - T) 2 + (S - U)  2)*((D - LL)  2 + (T - MM)              2 + (U - NN)                                                                  2) + ((D - LL)*(A - D) + (T - MM)*(R - T) + (U - NN)*(S - U))                 2)  .5 - ((D - LL)*(A - D) + (T - MM)*(R - T) + (U - NN)*                    (S - U)))/((A - D)  2 + (R - T)  2 + (S - U) 2)                               670 WWWW = (D + (A - D)*VV)                                                   680 XXXX = (T + (R - T)*VV)                                                   690 YYYY = (U + (S - U)*VV)                                                   700 IF D < A AND A <  WWW THEN GOTO 750                                       710 IF D > A AND A > WWW THEN GOTO 750                                        720 IF D < A AND A < WWWW THEN GOTO 790                                       730 IF D > A AND A > WWWW THEN GOTO 790                                       740 IF D = A THEN GOTO 830                                                    750 WW = WWW                                                                  760 XX = XXX                                                                  770 YY = YYY                                                                  780 GOTO 870                                                                  790 WW = WWWW                                                                 800 XX = XXXX                                                                 810 YY = YYYY                                                                 820 GOTO 870                                                                  830 IF T < R AND R < XXX THEN GOTO 750                                        840 IF T > R AND R > XXX THEN GOTO 750                                        850 IF T < R AND R < XXXX THEN GOTO 790                                       860 IF T > R AND R > XXXX THEN GOTO 790                                       870 ZZ = (YY*X - YY*V + W*XX - W*X + Y*V - Y*XX)/(WW*V - WW*X +               G*X - G*XX + J*XX - J*V)                                                      880 AAA = (YY*J - YY*G + W*WW - W*J + Y*G - Y*WW)/(XX*G - XX                  *J + V*J - V*WW + X*WW - X*G)                                                 890 BBB = ((ZZ) 2 + (AAA) 2 + (1)) .5                                         900 CCC = ((BB*ZZ) + (CC*AAA) + (1))/(FF*BBB)                                 910 DDD = (1 - (CCC) 2) .5                                                    920 EEE = ATN(DDD/CCC)                                                        930 FFF = ABS(EEE)*180/3.14159                                                940 FG = ((BB*WW) - (BB*LL) + (CC*XX) - (CC*MM) +                             (1*YY) - (1*NN))                                                              950 FH = ((FA*WW) - (FA*LL) + (FB*XX) - (FB*MM) +                             (FC*YY) - (FC*NN))                                                            960 IF (FG > 0) AND (FH > 0) THEN PRINT "ARC ANGLE                            FOR FIX POINT", CINT(FFF)                                                     970 IF (FG > 0) AND (FH < 0) THEN PRINT "ARC ANGLE                            FOR FIX POINT", CINT(-FFF) + 180                                              980 IF (FG < 0) AND (FH > 0) THEN PRINT "ARC ANGLE                            FOR FIX POINT", CINT(-FFF)                                                    990 IF (FG < 0) AND (FH < 0) THEN PRINT "ARC ANGLE                            FOR FIX POINT", CINT(FFF) - 180                                               1000 IF (FG <  0) AND (FH = 0) THEN PRINT "ARC ANGLE                          FOR FIX POINT", "-90"                                                         1010 IF (FG > 0) AND (FH = 0) THEN PRINT "ARC ANGLE                           FOR FIX POINT", "90"                                                          1020 IF (FG = 0) AND (FH < 0) THEN PRINT "ARC ANGLE                           FOR FIX POINT", "-180"                                                        1030 IF (FG = 0) AND (FH > 0) THEN PRINT "ARC ANGLE                           FOR FIX POINT", "180"                                                         1040 GGG = (J - G)*(WW - LL) + (X - V)*(XX - MM) + (Y - W)*(YY - NN)          1050 HHH = (((G - J) 2+(V - X) 2 + (W - Y) 2)                                  .5)*(((WW - LL) 2 + (XX - MM) 2 + (YY - NN) 2) .5)                           1060 III = GGG/HHH                                                            1070 JJJ = (1 - (III) 2) .5                                                   1080 KKK = ATN(JJJ/III)                                                       1090 LLL = KKK*180/3.14159                                                    1100 IF LLL < 0 THEN LLL = LLL + 180                                          1110 PRINT "SLIDE ANGLE FOR FIX POINT", CINT(LLL)                             __________________________________________________________________________

The program as set forth above has the following functional aspect:

10-160 Data (X,Y,Z) Entry

170-270 Gantry Tilt Correction of Data

280-300 Midpoint (Between EAC Points, Along Axis 67) Determination

310-340 Derivation of Vectors Describing Plane Through Fixed Arc andPlane Through EAC's and Burr Hole

350-400 Derivation of Angle Between Two Planes Above

410-450 Cross Product of Midpoint to Burr Hole Vector and EAC to EACVector

460-530 Spacial Conditions to be Satisfied to Determine Correct Slide(81, 82) Guide Angle

540-610 Determination of Slide Guide Angle

620-690 Determination of Intercepts of Line Through Target and Burr Holewith Sphere Created by Free Arc Rotation

700-860 Variable Conditions Applied to Determine Correct Intercept

870-1030 Derivation of Angle Between Fixed and Free Arcs for Acceptanceof Stereotactic Instrument Placement Guide (10, FIG. 1) Fixing Point 30(Similar to 310-530)

130-1110 Derivation of Slide Guide Angle for Accepting Fixed Point 30 ofStereotactic Instrument Placement Guide (10, FIG. 1) (Similar to540-610)

As can be seen from the computer program, it utilizes, in part, vectorparameterization, to correct for any non-zero angle of inclinationbetween imaging equipment and the patient while there is an incrementaladvance between images. Thus the gantry angle 43 is taken into account.

In a method of positively locating a burr hole site on a patient's skullduring a neurological procedure utilizing the guide frame 56, thefollowing steps are practiced:

(a) Coordinate multi-planar tomographic imaging (e.g. a CT scan) iseffected of the patient's head, as schematically illustrated in FIG. 6.

(b) During the practice of step (a) locations of the target in thepatient's head, the burr site on the patient's skull, the patient's leftand right auditory medati, and at least one of the patient's orbitalridges, are determined.

(c) With the computer 44 or 41, the data determined in step (b) is usedto calculate the angular positions (the angle 84) of the frame members57, 58 to correctly mark the burr hole site on the patient's skull.

(d) Then the ear fixations (that is rods 68, 69) are moved into positivecontact with the patient's ears (auditory medati), and the nasal bridgefixation 75 is moved into positive contact with the patient's nasalbridge.

(e) The second frame 58 of the guide frame 56 is then moved with respectto the first member 57 to the proper angular orientation 84 to mark theburr hole site, and moving the instrument guide 81 is moved to theproper position along the second frame member 58, and the burr hole siteis marked using the instrument guide 81 (as by passing a needletherethrough into contact with the patient's skull). Exemplary positionsfor marking the burr hole site utilizing the frame 56 are illustrated inFIG. 10, the burr hole site--when marked--being provided at 86 asillustrated in FIG. 12.

After practicing the above steps, the frame 56 may be removed from thepatient's skull, and the program first described with respect to thecalculator 41 utilized to determine the fixing point. Alternatively, themethod described above with respect to the frame 56 may be utilized forpositively locating the fixing point by the further step of (f) movingthe second frame member 58 with respect to the first frame member 57 tohave the proper angle 88 (see FIG. 12), typically about 160°-180° , forthe fixing point on the patient's skull, and then marking the fixingpoint using the instrument guide 81.

As yet another alternative, the element 10 from FIG. 1, as illustratedin FIG. 12, may be mounted directly with the frame 56 after the burrhole is formed at the burr hole site 86, as by bringing the point 30into contact with the end 89 of the instrument guide 81 opposite theinner end 85 thereof, while the skull engaging point member 11 isstabilized in the burr hole at the burr hole site 86. Thus in thisembodiment, the element 81 itself provides the fixing point. Thecatheter 26 may then be passed through the element 24 as describedearlier with respect to FIG. 5. Of course as also described earlier,instead of a catheter 26 another type of instrument may be utilized,passed to the target within the patient's skull (e.g. within one of theventricles).

The device 10 may be used without the frame 56, as illustrated in FIG.5, or with the frame 56, as illustrated in FIG. 12, depending upon whatis best for a particular situation, and the location of the burr holeand fixing point sites may be practiced using both the proceduredescribed above with respect to FIGS. 5 through 7 and the proceduredescribed with respect to FIGS. 10 through 12, or just one of theseprocedures.

Thus according to the invention a simplified method of performing aneurological procedure on a human patient utilizing a scanner, acerebral instrument guide frame, and an operating room, is provided.According to the invention it is not necessary to effect a second scan.Rather, the invention comprises the steps of substantially sequentially:

(a) Effecting coordinate multiplanar tomographic imaging (e.g. a CTscan) of the patient's head with the scanner while the patient's head isfree of frame attachments (see FIG. 6), to obtain data necessary forperforming a neurological procedure.

(b) Moving the patient to the operating room.

(c) In the operating room, utilizing the data from step (a), fixing thecerebral instrument guide frame (e.g. 56) on the patient's head (seeFIGS. 10-12).

And, (d) substantially immediately after step (c), in the operatingroom, without transporting the patient back to the scanner 40 to effecta second imaging, performing the neurological procedure on the patient,utilizing the cerebral instrument guide frame 56 to guide one or moremedical instruments (e.g. a catheter 26, light pipe, laser, etc.).

It is to be understood that the apparatus and procedures according tothe present invention are to be interpreted broadly in conformance withthe following claims, so as to encompass all equivalent procedures anddevices.

What is claimed is:
 1. A method of performing a neurological procedureon a human patient utilizing imaging equipment, a cerebral instrumentguide frame, and an operating room, comprising the steps ofsubstantially sequentially:(a) effecting coordinate multiplanartomographic diagnostic imaging of the patient's head with the imagingequipment while the patient's head is free of frame attachments, toobtain data necessary for performing a neurological procedure; (b)moving the patient to the operating room; (c) in the operating room,utilizing the data from the diagnostic imaging of step (a), fixing thecerebral instrument guide frame on the patient's head; and (d)substantially immediately after step (c), in the operating room, withouttransporting the patient back to the imaging equipment to effect asecond imaging, performing the neurological procedure on the patient,utilizing the cerebral instrument guide frame to guide one or moremedical instruments.
 2. A method as recited claim 1 wherein during thepractice of step (a) there is non-zero angle of inclination betweenimaging equipment and the patient and while there is an incrementaladvance between images; and wherein step (a) is practiced by thesub-steps of:(a1) during coordinate multiplanar tomographic imaging ofthe patient's body, determining the coordinates of a first point on orwithin the patient's body; (a2) during coordinate multiplanartomographic imaging of the patient's body, determining the coordinatesof a second point on or within the patient's body; (a3) determining thenon-zero angle of inclination of the imaging equipment with respect tothe patient and the incremental advance between images; and (a4)utilizing the coordinates of the first and second points, the non-zeroangle of inclination, and the incremental advance, by vectorparameterization calculating the distance between the first and thesecond points and the loci of points along a line containing the firstand second points.
 3. A method as recited in claim 2 wherein step (a4)is practiced by calculating the straight line distance between the firstand second points and the loci of points along a straight linecontaining those points.
 4. A method as recited in claim 2 wherein steps(a1) and (a2) are practiced by CT scanning.
 5. A method as recited inclaim 2 wherein the neurological procedure of step (d) is selected fromthe group consisting essentially of ventriculostomy, biopsy, radioactiveseed placement, and lesion generation.
 6. A method as recited in claim 1wherein the neurological procedure of step (d) is selected from thegroup consisting essentially of ventriculostomy, biopsy, radioactiveseed placement, and lesion generation.